In recent years, in diesel engines or in gasoline engines, those of in-cylinder direct injection system in which fuel at high pressure is directly injected in a cylinder for combustion have been developed for improved performance such as fuel-efficient, high output, and so on.
In such an engine of in-cylinder direct injection system requires a high-pressure fuel pump for pressurizing fuel to a high pressure, and such high-pressure fuel pump is provided with a sealing device for reciprocating movement in which high sealing property is required.
One of sealing devices for reciprocating movement in the related art is shown in FIG. 9. A sealing device 101 shown in FIG. 9 is employed for the purpose of sealing high-pressure fuel supplied from a high-pressure fuel pump used for an engine, which performs fuel injection, to the high-pressure side H, which is the side to be sealed, of a shaft 110 reciprocating in the axial direction.
In FIG. 9, the sealing device 101 is disposed at the end of a housing 111, so as to seal high-pressure fuel (gasoline, light oil, and so on), which is an object to be sealed, flown from the high-pressure side H and passed through a sliding portion of a shaft guiding portion of the housing 111. Also, sealed on the low-pressure side L of the sealing device 101 is oil intended for lubrication and cooling.
In addition, the sealing device 101 includes a metal ring 102 having a cylindrical portion 102a to be fitted on the outer periphery of an end of the housing 111, and a first and a second seal lips 103, 104 formed of rubber-like resilient body, each extending from an inwardly directed flange section 102b provided at the end of the low-pressure side L of the cylindrical portion 102a of the metal ring 102 toward the high-pressure side H and the low-pressure side L for sliding on the shaft 110.
However, in the sealing device in the related art shown in FIG. 9, in order to prevent fuel leakage due to excessive abrasion of the seal lip, damage of the rubber-like resilient body, and so on, which may be caused by increase in the pressure of the high-pressure fuel, it has been necessary to construct the pump in such a manner that the pressure of the high-pressure fuel relating to the sealing device is limited normally to 0 to 0.6 MPa.
Therefore, the rubber-like resilient body is thin and when it is subjected to the pressure of the high-pressure fuel of 1 MPa or higher, it may be broken abruptly upon operation.
Since the used fuel has no lubricity, the more the pressure of the high-pressure fuel increases, the more the seal lip is abraded in an abnormal manner, and thus fuel leakage is more likely to occur.
In the case of fuel containing alcohol, the rubber-like resilient body is swelled, and thus is lowered in hardness and strength, whereby abrupt breakage upon operation, or fuel leakage due to decrease of tightening margin of the seal lip may occur.
In addition, since the device is bulky, space saving could not be achieved.
On the other hand, elimination of a drain port is contemplated for simplifying the pump construction. However, since elimination of the drain port may increase the pressure of the high-pressure fuel, it cannot be eliminated for limiting the working pressure of the high-pressure fuel to 0-0.6 MPa, and hence simplification of the pump construction cannot be achieved.
In view of such problems in the related art as described above, it is an object of the present invention to provide a high-performance sealing device which is superior in pressure-resistance, and thus can realize prevention of breakage.